Adjustable electrical network



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. 1,572,992 G. CRIISfiQN ET AL I ADJUSTABLE ELECTRICAL NETWORK Filed Dec. 15, 1922 x i INVENTORS 6. Qalssan @LL 6765mm BY W ATTORNEY mane-.1 Feb. 16, 1926.,

UNITED 1 STATES PATENT- QFFIC E."

onoizeE CRISSO'N, or nacxnusac'x, NEW JERSEY, ,AND- LEE L. GLEZEN, or NEW BRIGHTON, NEW YORK, .ASSIGNORS TO AMERIQAN TELEPHONE A ND TELEGRAPH conrm, a companion or NEW roux.

ADJUSTNBLE ELEcrmcAr NETWORK.

Lppli-cation filed December 15,1922. Serial 1T0. 607,190.

To all whom: it may x Beit knownthat we, GEORGE Caisson-and LEE L. GLEZEN, residing at Hacken'sac'k and NewBrighton, in the counties of Bergen and Richmond and States of New Jersey and New York, respectively, have invented certain Improvements in Adjustable Electrical Networks, of which the following is a specification.

An object of our invention is to provide a newand improved network or artificial line and to make it adjustable as to one characteristic without disturbing it with respect to a certain other-characteristic. Another object is to provide ja network of constant resistance characteristic impedance but adjustable for attenuation between its input and output terminals. Another object is to make such a network with the same impedance characteristic at the out ut terminals and at the input terminals. till another object is to provide in a simple and ,economlcal manner for making the circuit changes involved in the ad ustments mentioned. All these and other objects of our invention-will become apparent on consideration of a special case which is disclosed in this specification by way of example. It

will be understood that the invention is defined in the appended claims. -Referring to the drawings, Figure 1 is a diagram of an adjustable cord circuit repeater embodying our invention, and Figs. 2 and 3 are. detail diagrams which will bereferred to in explaining the principle of our device. Referring to Fig. 1, this shows an adjust- "able cord circuit repeater for twmway op oration interposed between the "two lines L and L The balanced three-winding-trans iorniers T and T are provided for simultaneous two-way operation.

The artificial line A balances the line L.

the transformpontacts shown below these relays in Fig. 51.. The attenuated output from the network N goes from the taps a and (No the adjust-- able balanced potentiometer P and thence -;:to the repeating element R, which amplifies these currents and sends them to the line The input for L and the 'artificialline A through the transformer T The apparatus just described has] relation to repeating from L to L and this involves the network N. Repeating the opposite armatures and contacts shown above these relays in Fig. 1. To avoid repetitionfthc structure and operation of the system will be flesiribed principally for repeating from L The repeater herein disclosed is intended for interposition between any one of several incoming lines L, L'-or L, and any one of severaloutgoing lines L L or L Accordingly, as different connections are made, a difi'erent net gain or amplification will be desired, and the repeateris arranged so that the net gain can be quickly adjusted. This net gain is equal to the gain to which the repeater is V tentiometer P, minus the loss' in the net'- work N.

This network Nmust be symmetrical with ployed in Fig. 1, and this type must be pre- Moreover, at all served at all adjustments. ad ustments the network must match the impedance of the line or other apparatus to which it is connected. This condition is expressed in Fig. 3 by the impedance value 2, which .is the same looking in the direction of the two arrows at the places where they appear in the drawing. With the notation indicated in Fig. 3 it can readily be shown that this requirement of the same input and output impedance leads to the equation,

. (a Also by Kirchhoffs laws ohms, work of Fig. 2, but it is obtained as the re- Eliminating i from equation 2,

Substituting in equation 1, the result is reached that I Equations 4 and 5 us to compute. the proper values for ;v and y in terms of e for any desired loss ratio a, and in this way the following table is obtained, assuming that the impedancee is 300 ohms:.

Miles 0 0 33 w on The value 300 ohms for y is obtained by taking half the impedance of the line L, which is assumed to be (100 ohms. Looking into the line L from the points a and cl, it wvill be seen that the line L and the artificial line A are in parallel and hence the impedance across those points is half the impedance of the line L. c 4

In order to get the ditterent adjustments represented in-t-h-e foregoing table by means of simple switching apparatus, the network is arranged as shown in Fig. 1 and also otherwise shown 'in Fig. 2. It will be seen that the. first decrement of 0", namely 38 is not represented directly in the netsultant of 41 ohms and 150 ohms in parallel. Accordingly, when the change is made from 6 miles loss to 4 milesloss, thisis accom plished by the throw of the single switch 61 from contact 62- to63, which operates to shunt out the 41011111 component and also to throw the 450 ohm component over to make it a part of the resistance 1 between the points a and cl. Similarly it will beseenthat the decrement 34 ohms is not rep-' resented directly in Fig. 2, but is obtained as the resultant of 35 ohms and 1360 ohms in parallel, and that the throwing of the single switch .71 shunts out the 35 ohm component troller 5 to positions 3 and 4 change the networkto give it the respective losses of 2. standard miles and 0. But

' pedance, having shunt. and series elements so related as to make the impedance the same looking.- either way from either element of apparaand transfers the 1360 ohm component into the g branch of the network.

Figs. 1 and Qar'e numbered in correspondence, so that the network can-be studied on both of them together. At the outset the relays and switches are all in the condition shown-inFigs. 1 and 2, and the full loss of (5- standard miles is interposed. At this time the controller arm 5 is at the initial position 1 asshownin Fig. 1. A move to position 2 closes the circuit of relay 6, throwing switches 61 and 61, and thus changing thenetwork, decreasing the series resistances a and increasing the shunt res-istancesy, so as to change the 'loss from 6 miles to 1 miles." It can readily be followedthrough that the. further steps of the conwill further throughall these changes the impedance .2. remains unchanged. "We claim:

1. A network with a pair of input terminals and a pair of-outp11t ter1ni11als and symmetrical with respect to said pairs I of'terminals and comprising a. series element and a shunt element, in combination with means to adjust those elements simultaneously' to vary the attenuation between input and output and keep the characteristic impedance unchanged.

2. In combinatlon -w1th two elements of apparatus of the same. characteristic 1ma network connected between them tus, and means to' adjust those elements simultaneously to vary the attenuation be tween input-. sggand' output and 'keep. the

characteristic impedance unchanged;

3. A network withia paii'- of input ter minals and a pair of output terminals and comprising a series impedance element and a shunt impedance element, in combination with means to reduce the magnitude of the series impedance and to transfer part of the series impedance element to increase the magnitude of the shunt. impedancev to adjust the attenuation between input and output and keep the characteristic impedance unchanged. a i

=1. A network with a pair of input terminals and a pair of output terminals comprising a series impedance and ashunt impedance, said series ing parallel elements,

impedance comprisand means to ad ustthe attenuation. by shunting one of said parallel elements and transferring the other to become a seriespart of the said shunt impedance. I

5. A network with a series impedance anda shunt impedance in combination with asingle switch with two opposite contacts of the shunt impedance.

adapted simultaneously to cutout series impedance and cut in shunt impedance by transferring elements used as series 1mincrease the shunt impedance.

' 6. A network with a series impedance and' a shunt lmpedance, In combination with a peda'nce'elements and connecting them to 'single switch with twoopposite cont-acts adapted simultaneously to cut out series impedance and cut 1n shunt mpedance by transferring elements used as series 1mpedance elements and connecting them toincrease the shunt impedance in proper proportion to keep the characteristic impedance of the network unchanged.

7. A network comprising a series impedance with certain elements in parallel and a shunt impedance, and a single switch with two alternative contacts to shunt one ofthe said parallelelements and vthrow the other parallel element in series as a part 8. The method of varying the series and shunt impedances of a network to keep its characteristic impedance constant, which consists in shunting one of two parallel elements in the series impedance and trans ferri'ng the other to a seriesrelation in the shunt impedance.

9. A network com risiim four im edanees connected in-rectangular' fashion with .the

opposite impedances equal and means to so as to keep the' characteristic constant for the network- 10. A network consisting of four imimpedance .pedance's arranged in rectangular fashion with the opposite impedances equal, certain elements of each impedancevo't one pair of opposites being in parallel and a switch to shunt, onesuch element and transfer another such element to a; series relation in the remaining side'sof the rectangle.

-1.1. A cord circuit repeateradaptedior interposition betweenvarious pairs of lines and requiring correspondingly different net gains'therethrough, said repeater comprising a. network with means to adjust it to keep its characteristic impedance unchanged hut vary its loss and thereby vary the net gain through the repeater, said network lying between two pairs of terminals and having the same physical character looking into it from one pair of terminals as -from the other;

In testimony whereof, We have. signed our names to this specification this 13th day o t December, 1922. v

GEORGE GRISSON. LEE GLEZEN. 

